The present invention relates to a blow-molding method and blow moldings, precisely to those that are lightweight but have good strength and good heat resistance and are therefore applicable to parts of inlet systems for internal-combustion engines for automobiles, etc.
Synthetic resins have many applications for various moldings in various fields. In particular, a blow molding process for them is much used for producing various containers, as the molding pressure for it may be low and as the molds for it are inexpensive. In the recent field of automobiles, the most important matter is to reduce the fuel consumption for saving resources and for solving environmental problems. To meet it, lightweight automobiles are much desired. For reducing the body weight of automobiles, many their parts are made of resin and not metal, and the conversion from metal to resin for them is remarkable these days.
For automobile parts, thermoplastic resins such as polypropylene resins and the like are used, as they are recyclable and applicable to various parts. However, the requirement for reducing the body weight of automobiles is being severer day by day. For reducing the weight of moldings for automobile parts, for example, the wall thickness of the moldings is reduced and the structure thereof is modified. For bumpers, fuel tanks, etc., blow molding is being employed in place of conventional injection molding.
Of such automobile parts, for example, those of inlet systems for internal-combustion engines must be highly resistant to heat, and producing them with polypropylene resins is proposed. For improving the strength, the rigidity and the heat resistance of polypropylene resins, inorganic fillers such as talc, calcium carbonate, glass fibers and the like are added to them. However, since the density of such inorganic fillers is high, the apparent density of the moldings containing them is inevitably high. Using such high-density fillers is against the requirement for lightweight automobile parts. In addition to the requirement of mechanical strength, heat resistance and weight reduction of moldings for the parts of inlet systems for internal-combustion engines, still another requirement now increasing for them is that they ensure noiseless surroundings inside automobiles for comfortable driving time and that their noise to the outside is as small as possible so as not to cause noise pollution.
To solve the problems, a resin composition is proposed in Japanese Patent Laid-Open No. 59233/1993, which comprises 100 parts by weight of a resin component prepared by mixing from 50 to 95% by weight of a polypropylene resin and from 5 to 50% by weight of a specific thermoplastic elastomer having vinyl-structured polyisoprene blocks, and from 10 to 150 parts by weight of an inorganic filler.
For molding the resin composition, therein disclosed is one example of injection-molding it into air hoses. However, when the inorganic filler content of the composition is low, the rigidity and the heat resistance of the moldings of the composition are poor; but when the content is high, the impact resistance of the moldings is low and the weight thereof increases. Therefore, the weight reduction of the moldings of the composition is limited. In addition, when the composition is molded into hollow moldings in a mode of injection molding, the mold for it requires a core, which, however, complicates the mold structure. As a result, the moldability is low and the molding cost increases.
The present invention is to provide blow moldings which are lightweight and have the advantages of high strength per weight, good rigidity, good heat resistance, good sound absorption, good heat insulation and good sound insulation, which are produced at low costs, and which are useful for the parts of inlet systems for internal-combustion engines, and also to provide an efficient method for producing the moldings.
In the situation as above, we, the present inventors have assiduously studied how to reduce the weight of moldings and to improve the quality thereof and what molding process is suitable for the intended moldings, and, as a result, have found that when a specific molding material is blow-molded under a specific condition, then lightweight and high-quality blow moldings having improved physical properties can be obtained. On the basis of this finding, we have completed the present invention.
Specifically, the invention relates to the following:
(1) A blow-molding method for fiber-containing thermoplastic resins, which comprises holding a parison made of an inorganic fiber-containing, melt-expandable thermoplastic resin, between a pair of facing splits of a mold, blowing the parison to shape it, and thereafter reducing the gaseous pressure inside it.
(2) A blow-molding method for fiber-containing thermoplastic resins, which comprises holding a parison made of a melt-expandable thermoplastic resin that contains a foaming agent and inorganic fibers, between a pair of facing splits of a mold, and blowing the parison to shape it.
(3) A blow-molding method for fiber-containing thermoplastic resins, which comprises holding a parison made of an inorganic fiber-containing, melt-expandable thermoplastic resin, between a pair of facing splits of a mold, and blowing the parison to shape it.
(4) The blow-molding method of above (1) to (3), wherein the inorganic fibers to be in the thermoplastic resin are selected from glass fibers, carbon fibers and metal fibers, and the fiber content of the resin falls between 15 and 70% by weight.
(5) The blow-molding method of above (1) to (4), wherein the parison is prepared by melt-kneading a molding material that contains at least fiber-reinforced thermoplastic resin pellets, and the pellets each have an overall length of from 3 to 100 mm, and contain from 20 to 90% by weight of inorganic fibers having a length equal to the overall length of the pellets and aligned parallel to each other in each pellet.
(6) The blow-molding method of above (1) to (5), wherein at least a part of the thermoplastic resin is modified with an unsaturated carboxylic acid or its derivative.
(7) A blow molding of a thermoplastic resin which contains from 15 to 70% by weight of inorganic fibers having a mean fiber length of from 1 to 20 mm and has a porosity of from 10 to 90%. (8) The blow molding of above (7), wherein the thermoplastic resin is selected from polypropylene resins, polyamide resins, polyester resins and polycarbonate resins.
(9) The blow molding of above (7) or (8), which is for the parts of inlet systems for internal-combustion engines.